The present invention relates to ultrasonic medical equipment, and in particular, to a method employable with such equipment to assess risk of coronary heart disease (CHD).
A key challenge in healthcare is identifying individuals who are at high risk for CHD and who thus would be candidates for intensive medical intervention either in the form of additional diagnostic testing or the initiation of proven therapeutic strategies.
One method of assessing risk of coronary heart disease is the Framingham Global CHD Risk Assessment (henceforth the xe2x80x9cFramingham Assessmentxe2x80x9d). See, xe2x80x9cPrediction of Coronary Heart Disease Using Risk Factor Categoriesxe2x80x9d, Circulation 1998; 97: 1837-1847 Wilson et al.
The Framingham Assessment, based on a long-term study of a population of individuals, relates age, cigarette smoking, blood pressure, total cholesterol and high-density lipoprotein (HDL) cholesterol, and diabetes to a quantitative risk of CHD typically expressed in a percent chance of having a CHD event (heart attack or cardiac death) in ten years. A drawback to the Framingham Assessment is that age dominates all other risk factors even though the risks of coronary heart disease between individuals of the same age can differ substantially. The explanation for the relationship between age and CHD events most likely is increasing coronary plaque burden that occurs with advancing age. For this reason, it is generally recognized that a measure of coronary plaque burden might provide a better indicator of the probability of developing coronary heart disease for an individual than age alone.
There are a number of methods of measuring coronary plaque burden, including measurement of carotid intima-medial thickness (CIMT) with B mode ultrasound sonography. Such measurements provide a non-invasive and highly reproducible technique for quantifying sub-clinical atherosclerosis.
Measurement of CIMT is currently not used widely as a clinical tool, however. In part, this is because there is no established relationship between various patient factors, CIMT, and quantitative risk of cardiac heart disease. Ideally, the Framingham study would be repeated, but the age replaced by a CIMT measurement. Unfortunately, such studies take many years to complete and the future study is hampered by ethical concerns resulting from our understanding of the significance of some of the risk factors. For example, given the knowledge of the relationship between CHD and CIMT, long-term monitoring without treatment of patients with high CIMT may not be possible.
The present inventors have recognized that a quantitatively rigorous relationship between CIMT and risk of CHD may be derived from the existing Framingham Assessment data by converting CIMT into an equivalent xe2x80x9cvascular agexe2x80x9d and substituting this xe2x80x9cvascular agexe2x80x9d for the chronological age used in the Framingham Assessment. The conversion of CIMT to vascular age can be done using studies that relate increase in CIMT to age in a standard population. One such study is the ARIC study described in xe2x80x9cHigh Resolution B Mode Ultrasound Scanning Methods in the Arteriosclerosis Risk in Community Study (ARIC) J. Neuroimaging, 1991; 1:68-73, Bond et al.
These latter studies generally show a range of CIMT values for individuals of a given age within the population and thus cannot be used to relate CIMT to actual chronological age. Nevertheless, vascular age may be equated to the age of the study population at which the given individual""s CIMT equals the population""s mean or other statistical center value. The concept of vascular age allows connection between these two disparate studies, for example, that of the Framingham Assessment and ARIC, to provide a quantitative relationship between CIMT and risk of coronary heart disease.
Specifically then, the present invention provides an ultrasonic diagnostic machine having an ultrasonic transducer that is positionable near the carotid artery to obtain echo signals from the carotid artery. A processing circuit communicating with the ultrasound transducer operates to process the echo signal to review the carotid intima-medial thickness (CIMT) and to apply the revealed CIMT to stored data relating CIMT of a population to a quantified risk of coronary heart disease (CHD). This quantified risk of heart disease is then output.
Thus, it is one object of the invention to provide the quantitative relationship between CIMT and risk of CHD such as may guide selection of treatment regimens.
The stored data used by the ultrasound machine may combine first data relating the CIMT to a vascular age and second data relating vascular age to quantified risk of CHD. The first data may be the ARIC data and the second data may be the data of the Framingham Assessment.
Thus, it is another object of the invention to establish a relationship between CIMT and risk of CHD using pre-existing studies.
The first data may relate multiple CIMT values to a given age but may be used to provide a single vascular age from a single CIMT value by a mathematical or statistical curve fitting process.
Thus, it is another object of the invention to employ existing studies describing CIMT as a function of age to create a virtual study relating CIMT values to vascular age.
The processing circuit may provide for input of patient data selected from the group consisting of: chronological age, gender, race, and body size. At least one of these patient data may also be applied to at least one of the first and second data sets.
Thus, it is another object of the invention to take advantage of the other patient input factors that may be used along with CIMT to establish quantified risk of CHD.
In one embodiment of the invention, the output from the ultrasound diagnostic machine may be vascular age.
Thus, it is another object of the invention to provide a simple unit for assessing CIMT data that can be readily understood by physicians and patients.
These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.